Implant for osteosynthesis device in particular of the backbone

ABSTRACT

The invention relates to an implant for an osteosynthesis device, in particular for the spine, the implant including a first assembly itself including: a fixing body having a housing for receiving the head of an anchor screw in such a manner as to define a ball joint; and a positioning ring; and a second assembly itself including a nut type system. According to the invention: the first assembly has a positioning ring mounted in the fixing body; and the second assembly has a nut type system, adapted, when tightened on the body, to bear against the bracing rod and to cause the positioning ring to move in linear displacement.

TECHNICAL FIELD

The present invention relates to the technical field of osteosynthesis,in particular of the spine, and more precisely it relates to an implantcomprising anchor screws in the vertebrae, designed to make it possibleto position angularly a bracing rod extending along said vertebrae forthe purpose of holding them stationary during a period of bone fusion.

PRIOR ART

Various systems have been developed for correcting and stabilizing thespine and for facilitating bone fusion at various levels of the spine.In one such system, a rod is placed along the spine and is held inposition by screws implanted in the vertebrae. The rod is suitable forbeing curved so as to follow the curvature of the region of the spine towhich it is fitted. Thus, in order to comply with the anatomical shapeof the spine, the bracing rod needs to be shaped so as to presentconsiderable amounts of curvature, particularly in order to enable it tobe installed relative to the lumbar and sacral vertebrae.

In order to make it possible for the rod to be shaped in this way whilealso ensuring that it is secured effectively to its anchor screws,proposals have been made to fit anchor screws with respective balljoints for receiving the bracing rod, so as to accommodateshape-following relative angles between the bracing rod and the anchorscrews.

Thus, by way of example, Europe an patent No. EP 0 614 649 describes animplant for an osteosynthesis device comprising a fixing body shaped inthe form of a socket in which a reception channel is formed to receive abracing rod. The fixing body is arranged to present a reception housingfor the head of an anchor screw in order to define a ball joint betweenthe anchor screw and the fixing body. That implant also has apositioning ring for placing between the head of the anchor screw andthe bracing rod. The implant also has a nut type system for assemblingthe bracing rod to the fixing body. Such a system has a nut screwed ontothe outside walls of the fixing body and a threaded lock screw isscrewed into the inside of the fixing body. By screwing such an assemblydevice tight it is possible to clamp firstly the bracing rod between thelock screw and the positioning ring, and secondly the anchor screwbetween the positioning ring and the fixing body.

It must be considered that such an implant is made up of a plurality ofparts that need to be built up into intermediate assemblies while theoperation is taking place. This gives rise to difficulties of assemblyand to installation time that is relatively lengthy.

Document DE 44 25 357 also describes an implant for an osteosynthesisdevice comprising a first assembly, itself comprising a fixing bodyarranged to present a reception housing for receiving the bead of ananchor screw in order to define a ball joint between the anchor screwand the fixing body. This first assembly also has a positioning ring forinterposing between the head of the anchor screw and the bracing rod.That implant further comprises a second assembly, itself comprising asystem of the nut type for assembling the bracing rod to the fixingbody. Such an implant does not enable effective connection to be ensuredbetween the anchor screw and the fixing body and therefore leads to thebracing rod being unstable relative to the anchor screw.

SUMMARY OF TE INVENTION

The object of the invention is thus to remedy the drawbacks of prior artimplants by proposing an implant for an osteosynthesis device of thespine comprising a bone anchor screw fitted with a ball joint forreceiving a bracing rod, such an implant being designed to be put intoplace quickly and easily, while also being adapted to enable aneffective and durable connection to be made between the bracing rod andthe bone anchor screw.

To achieve such an object, the implant for an osteosynthesis device, inparticular of the spine, comprises:

a first assembly comprising:

-   -   a fixing body for a bracing rod, said body being arranged to        present a reception housing for receiving an anchor screw head,        thereby defining a ball joint between the anchor screw and the        fixing body;    -   a positioning ring for interposing between the anchor screw head        and the bracing rod;

and a second assembly comprising a nut type system for fastening thebracing rod to the fixing body.

According to the invention:

the first assembly has a positioning ring mounted in the fixing bodywith freedom to move in limited linear displacement and allowing thebody and the anchor screw to rotate freely relative to each other in theabsence of the bracing rod; and

the second assembly has a nut type system adapted on being screwed ontothe body to bear against the bracing rod and move the positioning ringin linear manner so that on being tightened it clamps the bracing rodbetween said system and the positioning ring, and also clamps the anchorscrew between the positioning ring and the fixing body.

Various other characteristics appear from the following descriptiongiven with reference to the accompanying drawings which show embodimentsand implementations of the invention as non-limiting examples.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view showing a complete implant receiving anintervertebral bracing rod.

FIG. 2 is a perspective view of a first assembly forming the implant ofthe invention.

FIG. 3 is a section view in elevation of the first assembly, takensubstantially on lines III—III of FIG. 2.

FIG. 4 is a section view in elevation of an implant of the inventiontaken substantially on lines IV—IV of FIG. 1.

FIG. 5 is a perspective view of a second assembly making up the implantof the invention.

FIG. 6 is a section view of a second assembly, taken substantially onlines VI—VI of FIG. 5.

BEST MANNER OF PERFORMING THE INVENTION

The implant 1 shown in FIG. 1 is for an osteosynthesis device (notshown) in particular for the spine. In accordance with the invention theimplant 1 is constituted by a first assembly I comprising, inparticular, a bone anchor screw 2, and by a second assembly II designedto secure an intervertebral bracing rod 3 relative to the anchor screw2.

As can be seen more clearly in FIGS. 2 and 3, the first assembly Icomprises a fixing body 5 arranged to present a reception housing 6 forreceiving the head 7 of the anchor screw 2 which extends beyond the endof a threaded anchor rod 8 of longitudinal axis x. In conventionalmanner, the head 7 of the anchor screw 2 is generally in the form of asphere truncated at its summit and provided with a blind hole 9 ofpolygonal section to enable the anchor screw 2 to be turned by means ofa screw-driving tool that is not shown but that is conventional.

In the example shown, the fixing body 5 has a head 11 constituted in theform of a socket on a longitudinal axis y, with a cavity 12 formedtherein centered on the longitudinal axis y. In a preferred embodiment,two diametrally-opposite side branches or walls 13 project from thefixing head 11 so as to define between them a reception channel 14 forreceiving the bracing rod 3. The cavity 12 opens out into the channel 14between the side branches 13, via an orifice 15 formed through thebottom 16 of the cavity 12. The reception channel 14 opens out on eitherside of the head 5 in a direction that is perpendicular to the diametralplane of symmetry containing the side branches 12. The reception channel14 is preferably arranged in the top portion of the fixing head 11 so asto have a notch 18 of semicircular profile to enable part of the bracingrod 3 to be received therein, such a rod conventially being of circularcross-section.

The first assembly I also has a positioning ring 21 for interposingbetween the head 7 of the anchor screw and the bracing rod 3. Thispositioning ring 21 is mounted inside the cavity 12 and has a centralbore 22 of partly spherical shape opening out via a first transverseface 23 for cooperating with the top portion of the head 7 of the anchorscrew. Naturally, the greatest diameter of the central bore 22 issmaller than the diameter of the head 7 of the anchor screw. Thepositioning ring 21 is capable of limited displacement along the axis ofsymmetry y of the body 5 between the bottom 16 of the cavity 12 and thehead 7 of the anchor screw. In a preferred embodiment, the positioningring 21 is guided to move with limited linear displacement along thelongitudinal axis y. In the example shown, the ring 21 is guided to movein linear displacement by means of a guide peg 24 interposed between thefixing body 5 and the positioning ring 21. For example, the guide peg 24is engaged in blind bores formed in the bottom 16 of the cavity 12 and asecond transverse face 25 of the positioning ring extending facing thebottom 16 of the cavity.

It should be observed that the central bore 22 of the positioning ring21 opens out via a through opening 27 into the second transverse face 25so as to communicate with the orifice 15 formed in the head 11, therebyproviding access for a screw-driving tool to the blind hole 9 in theanchor screw. The second transverse face 25 of the positioning ring 21preferably presents a concave surface 28 complementary to the bracingrod 3. This concave surface 28 thus forms a kind of cradle continuingthe notch 18 so as to define a portion of the reception channel 14 forreceiving the bracing rod 3. It should be observed that the concave face28 lies automatically in line with the notches 18 for receiving thebracing rod 3 given that the positioning ring 21 is guided in lineardisplacement along the longitudinal axis y.

As can be seen more clearly in FIG. 3, the anchor screw 2 is heldassembled to the fixing body 5 by means of a closure cup 29 fixed to thefixing head 11. This closure cup 29 possesses a central bore 30 of partspherical shape complementary to the profile of the bottom portion ofthe head 7 of the anchor screw. The central bore 30 possesses a maximumdiameter which is naturally smaller than the diameter of the head 7 ofthe anchor screw. In the example shown, the closure cup 29 is fixed tothe fixing head 11 by means of a peripheral bead of welding 31. Theanchor screw 2 is thus mounted to the fixing body 5 via a ball jointmalting it possible for the fixing body 5 and the anchor screw 2 to moveangularly relative to each other within a cone. The head 7 of the anchorscrew 2 thus co-operates with the internal bores 22, 30 respectively ofthe positioning ring 21 and of the closure cup 29 so that together theydefine the housing 6 for guiding the head 7 of the anchor screw inrotation.

The way the assembly I is put together stems directly from thedescription above. The fixing head 11 is designed to receive thepositioning ring 21 in the cavity 12, while ensuring that the guide peg24 is engaged between the positioning ring 21 and the fixing head 11.The internal bore 30 of the closure cup 29 is engaged on the threadedend 8 of the anchor screw 2 and moves up to the head 7. The head 7 ofthe anchor screw 2 is inserted into the internal bore 22 of thepositioning ring 21. The closure cup 29 has the anchor screw 2 passingthrough it and it is fixed to the fixing head 11 by welding in theexample shown. It should be observed that in the absence of the bracingrod 3, the positioning ring 21 is free to move in linear displacementover a limited stroke so as to allow the head 7 of the anchor screw 2 torotate relative to the fixing body 5.

It should be understood that the anchor screw 2 is assembled to thefixing body 5 prior to being used. Thus, the assembly I is presented inthe form of a single unit ready for directly receiving the bracing rod 3which is fixed to the fixing body 5 by means of the second assembly IIwhich is a nut type fastener. In a preferred embodiment, the fastenerassembly II is a nut 33 of the type described in patent application WO98/41159.

In this preferred embodiment shown more particularly in FIGS. 4 to 6,the side branches 13 have outside walls 34 inscribed within a circle andthreaded to receive the nut 33 which, in conventional manner, has apolygonal outside section to enable it to be held by an appropriatetool. The nut 33 has tapping 35 for screwing onto the threaded walls 34of the side branches 13.

The nut 33 is fitted with a shoe 36 extending diametrally across thetapping 35 and mounted free to rotate relative to the nut 33 so as tocome to bear against the bracing rod 3 in order to hold it in place bybeing tightened between said shoe 36 and the positioning ring 21. Thewidth L of the shoe 36 is adapted to leave two gaps 37 on either side,each serving to pass one of the side branches 13 of the fixing body 5.The gaps 37 also make it possible to insert the two pins of a tool (notshown) for taking hold of the nut 33. The pins of the tool can bepositioned by engaging them in notches 38 formed in the sides of theshoe 36. In order to enable the pins of the tool to be guided andconsequently to enable the shoe 36 to be indexed between the sidebranches 13 even while it is out of sight, the inside walls of the sidebranches 13 have respective longitudinal slots 39 extending from thefree ends of the branches 13 as far as the fixing head 11.Advantageously, the shoe 36 has an inside transverse surface 40 that isconcave and complementary to the top surface of the bracing rod 3.

In an advantageous characteristic shown in FIGS. 5 and 6, the shoe 36 issnap-fastened to the nut 33. As can be seen in FIGS. 5 and 6, the nut 33has a peripheral groove 43 formed at the base of the nut for receivingribs 44 extending from opposite ends of the shoe 36 and suitable fordeforming elastically so as to snap-fasten in the groove 43.

The way the implant 1 of the invention, made up of two assemblies 1 and11, is used sterns directly from the above description.

The assembly I without the assembly II is initially used for implantingthe anchor screw 2 in a determined vertebra. Thereafter, the bracing rod3 is placed so as to be inserted between the side branches 13 of thefixing body 5. Given the freedom for relative rotation between theanchor screw 2 and the fixing body 5, the bracing rod 3 positions itselfautomatically inside the reception channel 14 of the body 5.

Thereafter, the nut 33 is screwed onto the outside walls 34 of the sidebranches 13 with the shoe 36 being engaged between the branches 13.Tightening the nut 33 causes the shoe 36 to move so as to come to bearagainst the bracing rod 3. Continued tightening leads to the positioningring 21 being subjected to limited linear displacement so as to exert aforce on the head 7 of the anchor screw 2. Such tightening of the nut 33leads to the anchor screw 2 being clamped between the positioning ring21 and the closure cup 29, and also to the bracing rod 3 being clampedbetween the shoe 36 and the positioning ring 21. It should be observedthat tightening the nut 33 onto the outside walls 34 of the sidebranches 13 ensures that they cannot splay apart when the shoe 36applies a thrust force on the bracing rod 3. This assembly makes itpossible to obtain large contact area between the shoe 36 and thebracing rod 3, thereby giving rise to effective and long-lastingclamping of the bracing rod 3 relative to the fixing body 5.

The invention is not limited to the examples described and shown sincevarious modifications can be applied thereto without going beyond theambit of the invention.

1. An implant for an osteosynthesis device, in particular for the spine, the implant comprising: a first assembly comprising: a fixing body for a bracing rod, said body being arranged to present a reception housing for receiving an anchor screw head, thereby defining a ball joint between the anchor screw and the fixing body; a positioning ring for interposing between the anchor screw head and the bracing rod; and a second assembly comprising a nut type system for fastening the bracing rod to the fixing body, wherein the first assembly has a positioning ring mounted in the fixing body with freedom to move in limited linear displacement and allowing the body and the anchor screw to rotate freely relative to each other in the absence of the bracing rod; and the second assembly has a nut type system adapted on being screwed onto the body to bear against the bracing rod and move the positioning ring in linear manner so that on being tightened it clamps the bracing rod between said system and the positioning ring, and also clamps the anchor screw between the positioning ring and the fixing body; wherein the positioning ring is guided to move with limited linear displacement relative to the fixing body by means of a guide peg co-operating with a complementary bore.
 2. An implant according to claim 1, wherein: the fixing body has two side branches defining a channel between them that opens out on either side of the body in order to receive the bracing rod, the side branches having outside walls that are threaded; and the fastening system comprises a nut adapted to be screwed onto the outside threaded walls of the side branches, the nut being fitted in its diametral zone with a shoe mounted to rotate freely and designed to come to bear against the bracing rod so that when tightened it clamps said shoe and the positioning ring.
 3. An implant according to claim 1, wherein the positioning ring presents a concave surface complementary to the bracing rod and is guided to slide in such a manner that the concave surface defines a portion of the reception channel for receiving the bracing rod so as to ensure that the bracing rod is positioned automatically between the side branches and on the positioning ring.
 4. An implant according to claim 2 or 3, wherein the positioning ring presents a through opening opening out between the side walls and over the head of the anchor screw in which there is provided a blind hole suitable for receiving a screw-driver tool passing through the opening.
 5. An implant according to claim 1 or 2, wherein the fixing body comprises: a fixing head on which there stands the two side branches and in which there is arranged a cavity opening out at one end between the side branches and opening out at its opposite end; the positioning ring mounted to move with limited displacement inside the cavity with its surface for receiving the bracing rod opening between the two side branches; the head of the anchor screw mounted at least in part inside the cavity so that the positioning ring is interposed between said head and the body; and a closure cup fixed on the fixing body on its inside face to close the cavity and having the anchor screw passing therethrough.
 6. An implant according to claim 1, wherein the positioning ring and the closure cup present partly-spherical bores so as to define the reception housing for receiving the head of the anchor screw.
 7. An implant according to claim 1, wherein the nut has a shoe of width adapted to co-operate with the nut to define on either side of the shoe two gaps serving firstly to receive the two pins of a tool for taking hold of the nut, and secondly to pass the side branches of the fixing body in order to enable said shoe to slide between the side branches.
 8. An implant according to claim 2 or 7, wherein the fixing body has two slots arranged facing each other in the inside walls of the side branches so that once the bracing rod has been installed they guide the pins of the tool on the fixing body and they enable the shoe to be indexed while out of sight between the side branches.
 9. An implant according to claim 8, wherein the nut has a shoe with two notches being formed on the side edges thereof, said notches opening out into the gaps and being designed to receive and position pins of the tool.
 10. An implant according to claim 7, wherein the nut has means enabling the shoe to be mounted by snap-fastening, which shoe is free to rotate relative to the nut once it has been mounted.
 11. An implant according to claim 4, wherein the positioning ring and the closure cup present partly-spherical bores so as to define the reception housing for receiving the head of another screw. 